1. Field of the Invention
The present invention relates to a testing system on an exchange that subscriber line or exchange itself provide to attain self-test in the inside of a built-in test circuit. More particularly, it relates to a test system for a voice-band data transmission interface (VDTI).
2. Description of the Related Art
Voice band Data Transmission Interface (VDTI) is widely used in Japan or international market, mainly. It is possible even for analog subscriber to link to an attached Called Customer Premises Equipment (CPE) for displaying information of a subscriber who sends an outgoing call, such as a caller number, called date or an identifier on the equipment.
As shown in a block diagram illustrating an outline of an outgoing call number displaying system employing VDTI in FIG. 12, information is transmitted between an analog telephone set 10, Called Customer premises Equipment (CPE) 11 and an network exchange 2 by a FSK (Frequency shift keying) signal. Caller information stored in network exchange 2 corresponding to caller 21 is modulated by a FSK (frequency shift keying) signal in a Called Line Identification (CLI) transmitter 3, which is a dedicated trunk. The modulated signal is transmitted to the subscriber, and is displayed on called customer premises equipment 11.
Service employing this caller number displaying function, such as a caller number informing system, has been brought by Nippon Telegram and Telephone Corporation (refer to Japanese laid open patent applications No. 4-165748 and 9-36962).
As an example of Bell-Core recommendations of FIGS. 13A and 13B, signal length or signal protocol is fully prescribed on VDTI. Therefore, it becomes difficult to provide a stable service on a nonstandard system.
FIG. 13A shows when a FSK signal is transmitted to the subscriber on On-Hook transmission status. Caller information is transmitted by a FSK signal for 2 or 3 seconds during a silent interval between a first ringing and a second ringing.
FIG. 13B shows when FSK signal is transmitted on an Off-Hook status. Off-hook means the subscriber disconnects a communication path once because FSK signal is transmitted while he is talking with other person. After procedures of a subscriber alerting signal (SAS), a CPE alerting signal (CAS) and an acknowledge signal (ACK) are executed between called line identification (CLI) transmitter 3, which is a FSK signal calling trunk, and called customer premises equipment (CPE) 11, a FSK signal is transmitted and the communication path is recovered.
Further, a FSK signal specification is prescribed in Bell-core recommendation as follows;
Modulation type: continuous-phase binary frequency shift keying
Logical 1 (Mark): 1200xc2x112 Hz
Logical 0 (Space): 2200xc2x122 Hz
Transmission Rate: 1200xc2x112 baud
Application of data: serial, binary, asynchronous
Transmission level: xe2x88x9213.5xc2x11 dBm
However, there are few techniques for testing normality of VDTI. Further, in the few techniques, only FSK signal modulation/demodulation circuit can be tested (for example, refer to Japanese laid open patent application No. 4-258061). By such the conventional techniques, only a closed section in Called line identification (CLI) transmitter 3, which is a FSK signal calling trunk, shown in FIG. 12, for example, the FSK modulation/demodulation circuit, could be tested. Therefore, it was only possible to test whether or not a FSK signal is present or what the output level is.
However, it is not enough for testing VDTI to test only the FSK modulation/demodulation circuit. There is required for testing VDTI with due regard to a transmission protocol on On-Hook or Off-Hook status. Further, the test should follow the standard of the signal length and data transmission.
Additionally, it is impossible to perform testing to cover widely range including communication paths in a network with regard to the protocol, in only a test of FSK signal modulation/demodulation circuit. Various devices are complicatedly controlled for currently-used service realized in an exchange.
There is a demand for testing not only each device but a network, communication paths and protocols in total. Further, there is a serious demand for realizing reliability of a system and supplying the service stably by automatically and regularly testing when there are many subscribers in a large-scaled network, such as an office exchange.
Therefore, it is an object of the present invention to provide a VDTI testing system on an exchange to achieve the above-described problem.
To attain the above-described problems, an exchange system for transmitting information, such as a caller number, to a subscriber line circuit by employing a frequency shift keying signal, the exchange system may include a loop circuit for imitating a loop of a subscriber""s telephone set, and a firmware for receiving a frequency shift keying signal and judging the normality of the frequency shift keying signal, wherein the firmware controls to open and close the loop circuit according to testing on On-Hook or Off-Hook protocol.
Further, as a feature of the detailed structure, a testing system on a voice-band data transmission interface on an exchange comprising an exchange including a central processing unit, and a signal transmission device which is controlled to transmit a test starting signal by the central processing, a caller line identification transmitter for receiving the test starting signal to output a frequency shift keying (FSK) signal, and line test equipment including a loop circuit which receives the frequency shift keying signal sent from the caller line identification transmitter and which is controlled to open or close according to a notification of a test result on On-Hook or Off-Hook protocol for detecting sufficiency to fulfill On-Hook or Off-Hook protocol, for the received FSK signal.